This application claims the priority of German Patent Document 198 10 288.7 filed Mar. 10, 1998 and PCT/EP99/01172 filed Feb. 23, 1999, the disclosures of which is expressly incorporated by reference herein.
The invention relates to a data bus for a plurality of nodes which exchange data messages among one another via at least one electrical line. The line may be a component of a star coupler. Such a data bus is known from the previously unpublished German patent application 19720401.
The circuitry of such a data bus may be implemented in the form of an open collector circuit. An open collector circuit has the disadvantage that, at high transmission rates and with many bus nodes, a relatively low resistance must be used as the collector resistance in order to obtain sufficient edge steepness of the signal messages which are present in pulse form. This leads to high currents and high sower dissipation and the necessity of using power transistors and resistors. A further problem results when at least one part of the nodes supplies optical messages.
Particularly if the number of bus nodes is large, signal amplification is required to supply the messages in an adequate quality to all nodes. For this purpose it is suitable to convert the messages into electrical form, to amplify them and to reconvert them into optical form. However, this double conversion with additional signal amplification, however, causes signal distortions that reduce data bus efficiency.
For a data bus designed as an open collector circuit, it is known in the art to provide signal shaping devices (cf. U.S. Pat. No. 5,684,831 A). Such a signal sloping device for each node results in high circuit complexity, particularly if there are many nodes.
The object of the invention is to create a data bus which provides interference-free bus communication with low circuit complexity even for a large number of optical bus nodes.
The invention consists of a logic decision gate and the signal conditioning circuit and their interaction. The decision gate does not require complex signal shaping devices for its use because it transmits the signals in their unchanged form. Moreover, the power requirement is low even if the number of nodes is large. The logic decision gate also makes it possible to significantly reduce the circuit complexity. It is only necessary to arrange a single signal conditioning circuit which models the output signal of the decision gate with regard to the pulse shape between the decision gate and the inputs of the nodes.
The shape of the output signal is matched to the shape of the input signal or of an adaptation as described in U.S. Pat. No. 5,684,831 A. The rising edges are flattened to make it possible to distinguish the useful signals from high-frequency noise signals with extreme edge steepness.
Embodiments of the invention are possible both with nodes that supply electrical data messages as well as with nodes that generate optical data messages. The latter nodes are connected to the data bus via opto-electric transducers in such a way that the signal outputs of the nodes are each routed to the decision gate via a transducer of this type, and the output of the decision gate is routed to the inputs of the nodes via a common electro-optical transducer or via individual transducers of this type.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.